Control for a two stage master cylinder

Abstract

A two stage master cylinder having a bore with a first diameter and a second diameter separated by a shoulder. A first piston is located in the first diameter of the bore to establish a first chamber. A second piston has a first section located in the first diameter of the bore to establish a second chamber and a second section located in the second diameter of the bore to establish an actuation chamber therein. A first passage in the second piston connects the actuation chamber with the second chamber. A second passage in the second piston connects the first passage to a reservoir in the housing. A shuttle piston located in the first passage has a first surface area exposed to the second chamber and a second smaller surface area exposed to the actuation chamber. A spring urges the shuttle piston toward the second chamber. An input force from an operator moves the second piston causing fluid to flow from the actuation chamber through the first passage to the second chamber. The first section of the second piston acts on actuation fluid and the operational fluid in the second chamber and the first piston acts on the operational fluid in the first chamber to provide the front and rear wheel brakes with a braking signal. The operational fluid in the second chamber acts on the first surface of the shuttle and overcomes the spring to establish communication of between the actuation chamber and the reservoir through the second passage. Thereafter, the entire input force from the operator acts on the first section of the second piston to pressurize the operational fluid in the first and second chambers in the generation of the braking signal.

I claim: 
     
       1. A two stage master cylinder comprising: a housing having a first diameter bore separated from a larger second diameter bore by a shoulder and a reservoir connected to said first diameter bore;   a first piston located in said first diameter bore and cooperating with said housing to define a first chamber in said first diameter bore;   a second piston having a first cylindrical body with a first diameter section extending from a second diameter section into said first diameter bore and cooperating with said housing and said first piston to define a second chamber in said first diameter bore, said second diameter section cooperating with said first diameter section, said shoulder, and said housing to define an actuator chamber in said second diameter bore, said first cylindrical body having a stepped axial bore extending through said first diameter section to a point adjacent said second diameter section, said first cylindrical body having a first radial passage for connecting said actuation chamber wtih said axial bore and a second radial passage for connecting said axial bore to said reservoir;   shuttle means located in said stepped axial bore of said first cylindrical body having a first surface exposed to the fluid in said second chamber and a second surface exposed to the fluid in said actuation chamber, said first surface being larger than said second surface, said shuttle means including a second cylindrical body having a first section separated from a second section by a second shoulder, said second shoulder cooperating with said stepped axial bore and the first section of said second cylindrical body to define a dampening chamber, a radial bore providing restricted fluid communication between the dampening chamber and the reservoir, the fluid pressure in said dampening chamber operating to control the rate of movement of said shuttle means;   first seal means associated with said shuttle means for controlling the communication of fluid from said stepped axial bore into said second chamber and said reservoir;   resilient means connected to said shuttle means for urging said first surface toward said second chamber; and   input means connected to said second piston and responsive to an input force for moving said first diameter section in said first diameter bore and said second diameter section in said second diameter bore to create an actuation fluid pressure in said actuation chamber and an operational fluid pressure in said second chamber, said actuation fluid pessure being communicated to said second chamber by flowing through said first radial passage into said stepped axial bore and around said first seal means, said operational fluid pressure acting on said first surface and moving said shuttle means in opposition to said resilient means and actuation fluid pressure acting on said second surface to communicate said axial bore to said reservoir and thereby relieve the actuation fluid pressure from said second bore to permit the entire input force to be communicated into said second piston means for moving said first diameter section in the first diameter bore and thereafter pressurize the fluid in the second chamber.   
     
     
       2. The two stage master cylinder, as recited in claim 11 wherein said second piston further includes: a first groove located between a first land and a second land, said second radial passage terminating in said first groove adjacent said first land, said first groove connecting said second radial passage with said reservoir upon movement of said second piston.   
     
     
       3. The two stage master cylinder, as recited in claim 2, wherein said second piston further includes: a second groove located on said first diameter section, said second groove being connected to said first groove to permit fluid communication between said actuation chamber and the reservoir upon termination of the operator input force.   
     
     
       4. The two stage master cylinder, as recited in claim 3, further including: second seal means having a lip which projects into said second groove, said lip engaging said first diameter section of said first cylindrical body to prevent communication of fluid from the actuation chamber to said first groove upon movement of said second piston means.   
     
     
       5. A two stage master cylinder comprising: a housing having a first diameter bore separated from a larger second diameter bore by a shoulder and a reservoir connected to said first diameter bore;   a first piston located in said first diameter bore and cooperating with said housing to define a first chamber in said first diameter bore;   a second piston having a first cylindrical body with a first diameter section extending from a second diameter section into said first diameter bore and cooperating with said housing and said first piston to define a second chamber in said first diameter bore, said second diameter section cooperating with said first diameter section, said shoulder, and said housing to define an actuator chamber in said second diameter bore, said first cylindrical body having a stepped axial bore extending through said first diameter section to a point adjacent said second diameter section, said first cylindrical body having a first radial passage for connecting said actuation chamber with said axial bore and a second axial passage for connecting said axial bore to said reservoir;   shuttle means located in said stepped axial bore of said first cylindrical body having a first surface exposed to the fluid in said second chamber and a second surface exposed to the fluid in said actuation chamber, said first surface being larger than said second surface;   first seal means associated with said shuttle means for controlling the communication of fluid from said stepped axial bore into said second chamber and said reservoir;   resilient means connected to said shuttle means for urging said first surface toward said second chamber; and   input means connected to said second piston and responsive to an input force for moving said first diameter section in said first diameter bore and said second diameter section in said second diameter bore to create an actuation fluid pressure in said actuation chamber and an operational fluid pressure in said second chamber, said actuation fluid pressure being communicated to said second chamber by flowing through said first radial passage into said stepped axial bore and around said first seal means, said operational fluid pressure acting on said first surface and moving said shuttle means in opposition to said resilient means and actuation fluid pressure acting on said second surface to communicate said axial bore to said reservoir and thereby relieve the actuation fluid pressure from said second bore to permit the entire input force to be communicated into said second piston means for moving said first diameter section in the first diameter bore and pressurize the fluid in the second chamber;   a first groove on said second piston located between a first land and a second land on the first diameter section of said first cylindrical body, said second radial passage terminating in said first groove adjacent said first land, said first groove connecting said second radial passage with said reservoir upon movement of said second piston;   a second groove on said second piston located on said first diameter section, said second groove being connected to said first groove to permit fluid communication between said actuation chamber and the reservoir upon termination of the operator input force;   second seal means located adjacent said shoulder on the housing having a lip which projects into said second groove, said lip engaging said first diameter section of said first cylindrical body to prevent communication of fluid from the actuation chamber upon movement of said second piston means; and   said shuttle means including a second cylindrical body having a first section separated from a second section by a second shoulder, said second shoulder cooperating with said stepped axial bore and the first section of said second cylindrical body to define a dampening chamber, said dampening chamber being connected to said first groove by a third radial passage in said first cylindrical body, said third radial passage metering fluid to said first groove to control the rate of movement of said shuttle means.   
     
     
       6. The two stage master cylinder, as recited in claim 5, wherein said shuttle means further includes: a first annular rib and a second annular rib on the first section of said second cylindrical body, said first and second annular ribs cooperating with said first section of said second cylindrical body and said first section of said first cylindrical body to define a control chamber in said stepped axial bore, said second cylindrical body having a control passage extending from said second surface to said control chamber, said actuation fluid pressure being communicated from said stepped axial bore into said control chamber through said control passage, said actuation fluid pressure acting on said second annular rib and moving the second cylindrical body to establish communication between said control chamber and said second radial passage and thereafter proportionally reduce the actuation fluid pressure in the actuation chamber to the fluid pressure in the reservoir.   
     
     
       7. The two stage master cylinder, as recited in claim 6, wherein said first seal means includes: a first lip seal located adjacent said first rib and a second lip seal located adjacent said second rib, said first lip seal allowing the actuation fluid pressure to freely flow from the control chamber to the second chamber while preventing the operational fluid pressure from being communicated into the control chamber.   
     
     
       8. The two stage master cylinder, as recited in claim 7, wherein said first piston includes: a third cylindrical body having an axial passage therethrough for connecting the first and second chambers with a pressure differential chamber contained therein, said third cylindrical body having a first and second axial slot located on the peripheral surface thereof.   
     
     
       9. The two stage master cylinder as recited in claim 8, further including: a bolt attached to said housing and extending through said first diameter bore into said first slot to prevent said third cylindrical body from rotating;   a movable wall located in said pressure differential chamber for preventing communication between said first and second chambers through said axial passage; and   a plunger connected to a switch attached to said housing, said plunger extending into said second slot in said third cylindrical body, said plunger responding to movement of said wall in said pressure differential chamber causing a predetermined difference between the fluid pressure in the first and second chambers to activate the switch and inform the operator of this pressure condition in the master cylinder.   
     
     
       10. The two stage master cylinder, as recited in claim 9, further including: a first valve located in a first outlet port of said first chamber for controlling the communication of the operational fluid pressure to the rear wheel brakes of a vehicle as a function of the input force; and   a second valve located in a second outlet port of said second chamber for metering the communication of the operational fluid pressure to the front wheel brakes of a vehicle as a function of the input force and thereby synchronize the operation of the front and rear wheel brakes.